So why do you suppose that black people typically vote Democrat?
Far from a simple thing to answer.
First and foremost likely family ties. Most casual political observers gain their initial feeling towards politics from their parents. Many voting age black people of today either lived during the Civil Rights movement or are childrens of members of the Civil Rights movement. In the time following that many of these individuals gravitated to support for the Democratic Party and thus in part out of loyalty/grattitude on the part of those living during it and in part based on history and family for the children, they continue voting that way.
Secondly, the majority of largely black political organizations in the country are left leaning in nature. This means blacks attempting to get involved with politics and identifying closely with their race are more likely to be brought into it from a liberal view point. This also helps establish the image, rightly or wrongly, that the Democrats cares about "black issues" while the Republicans do not. For casual voters, which makes up the majority of any race, this appearance could be enough to sway someone significantly.
Thirdly, as I pointed out in another post, unfortunantly for the black community a higher percentage of their people tend to utilize various entitlement programs that are typically championed by the left and condemned by the right. As such, human nature leads one to generally look more positively on things that helps oneself. That's not to say such a thing is right or wrong. But in general, if you're recieving some kind of social service you're more apt to view it as a good and necessary thing than someone who is not.
Fourthly, again as I pointed out with the Tea Party, image means a lot for casual voters. The Democratic Party is simply portrayed, rightly or wrongly, as the party for black people. Its similar to how they're portrayed similarly as the party for homosexuals, yet have had homosexuals in recent years say how the Democrats are simply using them by not dealing with many of their issues and just banking on them not voting Republican. The Democrats are viewed as the party move looking out for Black people, and thus its more likely that someone with little political knowledge will go that way because they believe that party is more in touch with the things they feel is important.
Fifthly, the different ideologies. Conservatism, though it doesn't always show it on a board like this, generally abhors a victim mentality. The belief that things are stacked against you so you deserve things to be balanced either equal or into your favor due to that. As such you don't normally see as many prominent Republican groups pushing say "Black" issues or "Woman" issues because often they simply see things as "Issues". This big tent, we're all the same, approach has its benefits and negatives but one of those negatives is it takes away the notion of identity grouping. While some argue its a bad thing, and at times I agree, it can also be a powerful one. Humans in many ways are hardwired to want to form into groups, cliques, societies, etc. Part of how humans do that is by identifying similarities, and race can be a powerful similarity. By forgoing the use of that as a form of recruitment you improve your message of generalized equality but you hinder yourself with the use of recruitment based on identity.
So, in general summary, my thoughts....
1) The after affects of the civil rights era
2) The prominence of left leaning black political organizations
3) The higher reliance on services supported by Democrats and opposed by Republicans
4) The perception, right or wrong, that the Democrats are more in touch with issues important to blacks
5) Conservative ideology making identity based recruitment less frequent than on the opposite side
I think all those things largely play into why many of the majority of the African American population tends to vote Democrat.
